Method for drying wood products in order to produce wood products with reduced voc emissions

Abstract

The disclosure relates to a method for drying wood products with reduced discharge of VOC.

1 . A process for drying wood products, wherein the process comprises the following process steps:
 a) providing a wood product,   b) drying the wood product by thermal treatment; wherein process step b) is performed in two stages and comprises at least the following steps:   b1) if applicable, adding steam to the wood product and drying the wood product by removing a first amount of steam; and   b2) drying the wood product by removing a second amount of steam until a predeterminable target moisture is reached, wherein   in process step b1), if applicable, steam is added in a predetermined first range of amounts and removed in a predetermined second range of amounts such that a lower limit and an upper limit of at least one of the first range of amounts and the second range of amounts are chosen depending on at least one specification of the wood product provided in process step a).   
     
     
         2 . The process according to  claim 1 , wherein a lower limit and an upper limit of at least one of the first and the second ranges of amounts are effected depending on the amount of wood provided in process step a) in the wood products. 
     
     
         3 . The process according to  claim 1 , wherein a lower limit and an upper limit of at least one of the first and the second ranges of amounts are effected depending on the amount of VOCs contained in the wood product provided in process step a). 
     
     
         4 . The process according to  claim 3 , wherein the amount of VOCs contained in the wood product provided in process step a) is determined by an examination of the wood product used or is estimated based on the type of the wood product used, in particular the wood contained. 
     
     
         5 . The process according to  claim 1 , wherein the total amount of steam removed in process step b1) is in a range of amounts from 0.5 to 100 times the mass based on the amount of VOCs of the provided wood product. 
     
     
         6 . The process according to  claim 1 , wherein the total amount of steam separated in process step b1) is in a range of amounts from 0.001 to 0.2 times the mass based on the dry mass of the provided wood product. 
     
     
         7 . The process according to  claim 1 , wherein no steam is added in process step b1). 
     
     
         8 . The process according to  claim 3 , wherein at least one of terpenes and fatty acids is considered as VOCs. 
     
     
         9 . The process according to  claim 1 , wherein process step b1) is at least partially performed under the exclusion of air. 
     
     
         10 . The process according to  claim 1 , wherein steam removed in process step b1) is continuously removed from the process at at least one steam emission location. 
     
     
         11 . The process according to  claim 1 , wherein the VOC-containing steam removed according to process step b1) is collected and, if applicable, one or more components are further treated. 
     
     
         12 . The process according to  claim 11 , wherein, as further treatment, a mixture of terpenes or turpentine oil is isolated. 
     
     
         13 . The process according to  claim 11 , wherein, as further treatment, a mixture of fatty acids or other organic substances is isolated. 
     
     
         14 . The process according to  claim 11 , wherein, as further treatment, a hydrolate is isolated. 
     
     
         15 . The process according to  claim 11 , wherein the separated steam or one or more components are further treated by combustion or exposure to high temperatures, adsorption, absorption, membrane technology techniques, condensation, or crystallization. 
     
     
         16 . The process according to  claim 1 , wherein at least one of the heat of a material flow occurring in the process and the heat of a separated steam flow is energetically reused in the process. 
     
     
         17 . The process according to  claim 1 , wherein the process steps b1) and b2) are performed in two consecutive drying devices. 
     
     
         18 . The process according to  claim 1 , wherein the wood product is a wood-containing product produced in a dry process. 
     
     
         19 . The process according to  claim 1 , wherein the drying in the first drying stage is performed at a temperature ≥100° C. 
     
     
         20 . The process according to  claim 1 , wherein the drying in the first drying stage is performed in a circulating air mode, in which the released vapours remain substantially within the drying device. 
     
     
         21 . The process according to  claim 20 , wherein the fresh air fraction in the circulating air mode is 20%, based on the total volume of the drying device of the first drying stage. 
     
     
         22 . The process according to  claim 1 , wherein the supply and/or discharge of the wood products into or out of the first drying stage are performed via a substantially airtight lock.